Syndrome de sécrétion inappropriée d'hormone antidiurétique : diagnostic et prise en charge

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the commonest form of dilutional hyponatremia. The primary pathogenic mechanism is the excessive arginine vasopressin release causing renal water reabsorption and resulting in hyponatremia with expansion of extracellular fluid volume. The diagnosis of SIADH is based on the five following criteria: hypotonic hyponatremia, urine osmolality in excess of plasma osmolality, absence of oedema or volume depletion, increase renal sodium excretion and normal thyroid, adrenal or renal function. Many conditions have been associated with SIADH, which may be classified into four major groups: neoplasia, neurological disorders, lung disease, and an increasing variety of drugs. The symptoms of hyponatremia are mainly neurological, the severity of which being related to both the absolute serum sodium level and its rapidity of fall. The management of SIADH patients included the satisfactory treatment of the underlying cause and the removal of the excess total body water. The correction of hyponatremia has to take into account the risk of appearance of osmotic demyelination syndrome. Thus, in most guidelines rapid correction of hyponatremia is only indicated in patients who develop acute hyponatremia or in patients with severe symptoms. Fluid restriction remains the safe mainstay of management of chronic hyponatremia. The vasopressin V2 receptor antagonists offer a new therapeutic approach.